video: msmfb: Put the partial update magic value into the fix_screen struct.

This can then be tested by userspace to see if the capability is supported.
Userspace cannot rely on that value being left in var_screen, since userspace
itself can change it.

Signed-off-by: Dima Zavin <[e-mail]>
Signed-off-by: Carl Vanderlip <[e-mail]>
Signed-off-by: David Brown <[e-mail]>

drivers/video/msm/msm_fb.c

···
 	fb_info->var.yoffset = 0;
 
 	if (msmfb->panel->caps & MSMFB_CAP_PARTIAL_UPDATES) {
+		/*
+		 * Set the param in the fixed screen, so userspace can't
+		 * change it. This will be used to check for the
+		 * capability.
+		 */
+		fb_info->fix.reserved[0] = 0x5444;
+		fb_info->fix.reserved[1] = 0x5055;
+
+		/*
+		 * This preloads the value so that if userspace doesn't
+		 * change it, it will be a full update
+		 */
 		fb_info->var.reserved[0] = 0x54445055;
 		fb_info->var.reserved[1] = 0;
 		fb_info->var.reserved[2] = (uint16_t)msmfb->xres |